1. Field of the Invention
The present invention relates generally to a centralized scheduling method and apparatus for minimizing inter-cell interference in a heterogeneous network including a macro Base Station (BS) and lower power Local evolved Node Bs (LeNBs), and more particularly, to a centralized scheduling method and apparatus for minimizing inter-cell interference in the wireless communication system adopting femto-eNB-based service coverage expansion (range expansion).
2. Description of the Related Art
In order to increase the coverage and capacity of a macro BS-only network, extensive research has been conducted to deploy LeNBs, particularly in association with the 3rd Generation Partnership Project Long Term Evolution-Advanced (3GPP LTE-A). For example, the coverage expansion can be achieved with a Heterogeneous Network (HetNet) implemented by deploying Remote Radio Heads (RRHs), pico or femto cells, or relays within the coverage of a macro cellular network.
A HetNet is capable of achieving a more gainful spatial reuse effect through cell splitting. However, the significant difference in transmission power between the macro and micro eNBs increases inter-cell interference.
Recently, a method for expanding the coverage of the micro eNB by offloading the macro eNB to the micro eNB has been disclosed to improve the capacity and fairness of the HetNet.
One approach for coverage expansion of the micro eNB is to increase the Transmission (Tx) power of the micro eNB and have each terminal attach to the eNB transmitting the single with the strongest Downlink (DL) Received Signal Strength (RSS) in the cell selection procedure. In the case, however, both the macro and LeNB terminals are likely to experience significant interference.
Another approach for coverage expansion of the micro eNB is to give the DL RSS of the micro eNB a positive offset (range expansion bias). In this case, the terminal selects the micro eNB to which it is nearer than the macro eNB, although the DL RSS of the macro eNB is stronger than that of the micro eNB. Accordingly, it is possible to expand the coverage of the micro eNB without increasing its transmission power.
However, the terminal attached to the micro eNB within its expanded area is likely to be influenced by significant inter-cell interference from the macro eNB having the stronger DL RSS than that of the micro eNB.
The coverage expansion of the micro eNB is capable of improving the capacity of the macro eNB by offloading the macro User Equipment (UEs) to the micro eNB. However, the low link performance of the UE located in the range expansion area of the micro eNB causes degradation of the sum capacity of the network.
To this end, there has been disclosed a multi-cell cooperative transmission technology to improve cell edge performance by mitigating the inter-cell interference, otherwise known as Coordinated Multi-Point transmission and reception technology (CoMP) under discussion in the 3GPP LTE Rel. 11 standard. The aforementioned problems, however, also may occur in the CoMP scenarios 3 and 4, i.e. CoMP scenarios in the HetNet environment.
In CoMP scenario 3, the multiple TPs (Transmission Points or low power RRHs) participating in coordination within the macro cell coverage have a different PCID from that of the macro cell. In CoMP scenario 4, the multiple TPs participating in coordination within the macro cell coverage have the same PCID as the macro cell.
FIG. 1A illustrates a conventional HetNet which causes significant inter-cell interference. As shown in FIG. 1A, the conventional HetNet includes macro eNBs 110, 112, and 114, micro eNBs 116, 118, 120, 122, 124, 126, and 128, and UEs 130, 132, 134, 136, 138, 140, 142, 144, 146, and 148. Reference numerals 102, 104, and 106 denote the coverage of macro eNBs 110, 112, and 114, respectively.
In the HetNet of FIG. 1A, the coverage of each of the micro eNBs 116, 118, 120, 122, 124, 126, and 128 has been expanded. Reference numeral 108 denotes the range expansion area of the micro eNB.
Reference numeral 150 denotes a desired signal between the UE and the eNB. In FIG. 1A, the UEs 130 to 134 are scheduled by the macro eNBs, while the UEs 136 to 148 are scheduled by the micro eNBs.
In FIG. 1A, reference numeral 152 denotes inter-cell interference. As shown in FIG. 1A, it is noted that all of the UEs are experiencing significant inter-cell interferences in the conventional HetNet.
FIG. 1B illustrates the conventional HetNet with blanked macro eNBs. Compared to FIG. 1A, some of the inter-cell interferences in FIG. 1B are removed by blanking the macro eNBs.
The macro eNBs are blocked in the HetNet of FIG. 1B as compared to FIG. 1A, which indicates that the macro eNBs have stopped data transmission. Accordingly, the inter-cell interferences from the micro eNBs and neighbor macro eNBs to the macro UEs 130, 132, and 134 have been canceled.
Accordingly, there is a need in the art of enhanced cell association and Inter-Cell Interference Coordination (ICIC) technologies for efficient operation of the HetNet.